1. Field of the Invention
The present invention relates to systems configured for providing advanced telephony-type services for subscribers in a voice over Internet Protocol (IP) network according to H.323 protocol.
2. Description of the Related Art
The evolution of the public switched telephone network has resulted in a variety of voice applications and services that can be provided to individual subscribers and business subscribers. Such services include voice messaging systems that enable landline or wireless subscribers to record, playback, and forward voice mail messages. However, the ability to provide enhanced services to subscribers of the public switched telephone network is directly affected by the limitations of the public switched telephone network. In particular, the public switched telephone network operates according to a protocol that is specifically designed for the transport of voice signals; hence any modifications necessary to provide enhanced services can only be done by switch vendors that have sufficient know-how of the existing public switched telephone network infrastructure. Hence, the reliance on proprietary protocols and closed development environments by telecommunications equipment providers has limited service providers to vendor-specific implementations of voice and telephony services.
Voice over IP technology is under development as part of an alternative open packet telephony communications network, distinct from the public (circuit switched) telephone network, capable of using packet switched networks for integrating voice, data, facsimile, and Internet services, and the like. New packet telephony voice services are being built from open standards such as The International Telecommunications Union (ITU) Recommendation H.323. Recommendation H.323 defines the components, procedures, and protocols necessary to provide audiovisual communications on local area networks. Recommendation H.323 is based on the Real Time Protocol/Control Protocol (RTP/RTCP) of the Internet Engineering Task Force (IETF), and applies to either point-to-point or multipoint sessions, and references many other ITU recommendations, including H.225 and H.245. Recommendation H.225 specifies messages for call control including signaling, registration and admissions, and packetization/synchronization of media streams. Recommendation H.245 specifies messages for opening and closing channels for media streams, and other commands, requests and indications.
However, the existing H.323 standard does not specify features that provide flexibility for deployment of an IP-based system that supports advanced application services such as unified messaging. In particular, unified messaging involves presenting subscribers with messages in a prescribed format, even if the messages are stored in a different, incompatible format. For example, a messaging subscriber accessing a unified messaging system via telephone may rely on a text to speech converter to convert text-based messages such as e-mail messages into speech. Existing text to speech software processes currently have native support only for G.711 codecs: G.711 is an international standard for encoding telephone audio on a 64 kbps channel. However, G.729 (or G.729A) and G.723 are alternative standards for encoding toll quality telephone audio on an 8 kbps channel and 6.4 kbps channel, respectively. Hence, if a service provider wishes to deploy a voice over IP network that takes advantage of compression schemes such as G.729A or G.723 to conserve resources such as disk space for voice messages, the unified messaging system needs to support multiple codecs in a scalable manner.